In the 1950's, as seismologists began to assemble detailed elastic velocity versus depth models of the Earth, the subject of the physical properties of minerals at the high pressure and high temperatures of the Earth's interior began to receive considerable attention. This area of geophysics research, now called mineral physics, has historically been concerned with supplying information on mineral properties to allow the seismic velocity versus depth profiles in the Earth to be interpreted in terms of composition, mineral structure, and temperature. Experimental methods that can be applied to this problem include both static compression and dynamic (or shock) compression.
In 1967, the late Professor Tom Ahrens established a laboratory to study the dynamic compression of minerals. The lab moved to its present home on the main Caltech campus in 1974 with the help of a gift from Helen and Roland Lindhurst. The main facilities include three large guns, able to accelerate projectiles to speeds as high as ~7.5 km/s, and a variety of diagnostic tools to observe the interactions that result when the projectiles hit stationary targets.
Measurements of the velocity of projectiles and of the passage of shock waves through material, as well as the radiant temperature of shock-heated material, allow us to study the thermodynamics and phase relations of minerals and melts under deep planetary conditions. The shock wave measurement of equations of state (that is, the functional relationship among pressure, density, and temperature) is fundamental to Earth science because the different densities of Earth materials drive motions — such as convection in Earth's layers, plate tectonics, and volcanic eruptions — and, over time, these motions cause chemical evolution of the planet. Shock wave experiments are particularly essential for defining equations of state because pressure and density can be determined as absolute quantities and then form the basis for calibrating all the solid medium pressure markers used in static experiments. We also identify phase changes, including melting and the formation of dense, high-pressure minerals.
In addition to real-time experiments where we see the shock propagate through a target, a great deal of effort in the lab has been dedicated to "recovery experiments". In this configuration, a sample is embedded in a chamber so that we can recover it for detailed study after shock and release.
Prof. Ahrens was principal investigator of the lab from its founding until his retirement in 2006. Since that time, Prof, Paul Asimow has run the facility. Research over the years has included both terrestrial and planetary applications. We study equations of state of rocks, minerals and melts; examine the effects of shock deformation on minerals and rocks; identify and characterize shock pressure-induced phase changes; look at the energetics and geometry of impact cratering; synthesize novel materials; and interpret the collisional history of meteorites.
Over the years many students, postdocs, and visitors have trained or conducted collaborative experiments in the lab. Many of these former denizens are now leaders in mineral physics throughout the world.